New polymer syntheses, 101 Liquid-crystalline hyperbranched and potentially biodegradable polyesters based on phloretic acid and gallic acid

Three series of randomly branched copolyesters were prepared from mixtures of acetylated trimethylsilylesters of non-toxic natural hydroxy acids. The first series is based on 1:1 molar ratio of beta-(4-hydroxyphenyl)propionic acid (HPPA, phloretic acid) and 4-hydroxybenzoic acid (4-HBA). The second series was prepared from HPPA, 4-HBA and vanillic acid (VA, molar ratio 1:1:1), and in the third series VA was replaced by 4-hydroxycinnamic acid (HCA). The branching density was varied via the feed ratio of triacetylgallic acid. The stability of the nematic phase increases with decreasing branching density, but a partial LC-character was found even at relatively short length of the linear chain segments. Finally, two star-shaped and hyperbranched copolyesters were prepared. The incorporation of a star center type molecule allowed the control of the molecular weight, but eliminated the liquid-crystalline character almost completely. The ternary copolyesters and the quaternary copolyesters of VA were characterized by dynamic rheological measurements, and in the latter case also a few stress-strain measurements were conducted.